One type of electrical submersible pump assembly for oil wells includes a centrifugal pump that is coupled to an electrical motor. The pump has a large number of stages of impellers and diffusers. Normally, the pump assembly is lowered into the well on a string of tubing and, during operation, discharges the well fluid up through the tubing to the surface. The well fluid flows through perforations, past the electrical motor for cooling, and then enters the intake of the pump.
Often the well fluid is made up of water, oil and gas. Gas entrained in the well fluid may have a damaging effect on the ability of the pump to pump the well fluid. Significant amounts of gas or a gas slug can cause the pump to gas lock. A number of methods have been developed to re-route the gas so that it passes the pump intake. In one technique, a gas separator is installed in the pump assembly below the intake and above the motor for separating gas before entering the pump. A common type of gas separator has a rotating vane that separates gas from liquid by centrifugal force. Normally the gas flows to the annulus in the casing, and the remaining liquid portion of the well fluid flows up into the intake of the pump.
A number of other systems have been proposed to reroute the well fluid so that the gas passes the pump intake. In some techniques, a packer is set in the casing to isolate the separated gas from the well fluid being drawn into the intake. Usually, the packer is set in advance by a conventional method, then the pump assembly is lowered into the well, and a stinger on the lower end stabs into the packer.